What Does P0420 Code Mean on Chevy Silverado? Causes and Fixes
The P0420 is another common Onboard Diagnostic (ODBII) Code installed in the most modern Chevy Silverado engines.
The P0420 code on any Chevrolet Silverado mainly flashes to indicate that the Catalytic System Efficiency is below the Threshold on Bank 1 due to either a flawed Catalytic or faulty 02 oxygen sensors.
Once you notice or see the P0420 DTC code flashing, do not panic because it’s a pretty commonly seen error code. Just read this article throughout the end and follow the instructions provided in today’s article.
What Does P0420 Code Mean On Chevy Silverado?
Technically, the P0420 code on Chevy Silverado vehicle means the Catalytic System of the vehicle is not functioning efficiently and is Below the Threshold (Bank 1).
The P0420 code on Chevy Silverado indicates that the Engine Control Module of your vehicle has detected a potential issue with the Catalytic converter.
Quickly check out the dissection of the P0420 code:
- p- Powertrain (the system of components that drive the Chevy Silverado forward)
- 0-Generic malfunction code generated by PCM
- 4-Specific System related to the Catalytic system efficiency
- 20-The specific error information indicates under performance of the Catalytic system on Chevy Silverado caused by any issue with the exhaust or fuel system.
Chevy Silverado V6 and V8 engines have two catalytic converters. Each catalytic converter has two oxygen sensors. One of them is located upstream or front and another oxygen sensor is placed downstream or rear of the catalytic converter.
What is the purpose of Catalytic Converters on Chevy Silverado Engines?
The catalytic converters are mainly responsible to destroy harmful particles or pollutants built during the engine’s combustion cycle.
The catalytic converter uses refined platinum and gold meshes to filter the fumes and reduces exhaust pipe emissions.
What Triggers this P0420 Error Code on Chevy Silverado?
When the front or upstream oxygen sensor is working accurately, the reading is supposed to show fluctuation because there must be a difference between the reading of your Chevy vehicle’s regular operating temperature and when you are operating it in a closed loop.
Thus, when the reading of front 02 sensors has the same results in both situations, it indicates an obvious problem with the Catalytic converter.
Similarly, when the rear or downstream sensor shows steady voltage reading it means the sensor is working correctly.
But when it starts to fluctuate, like the front oxygen sensor, it indicates that the oxygen level is too high.
That’s when PCM generates the P0420 to notify Chevy users about the error.
How Serious Is Code P0420 On Chevy Silverado?
The code P0420 is not a serious or emergency warning code.
In most cases, drivers or users even do not experience any drivability problems while the P0420 error code flashes on the Chevy vehicle.
But if you ignore addressing and servicing your vehicle for too long, the damage severity level of the catalytic converter will increase, and over time, it might damage the internal engine and other related components (in the worst scenarios).
You won’t experience any major engine malfunctioning or underperformance issue while the P0420 code flashes.
However, you will eventually notice that your Chevy Silverado has started to emit the worst emission, which is also bad for the environment.
Even the repair of this code is considerably expensive, so that’s another reason not to overlook this error code on Chevy Silverado.
Thus, I highly suggest that once you have witnessed the P0420 code on your vehicle, do not ignore the code and service your vehicle promptly.
What Causes Code P0420 On Chevy Silverado?
Let’s have a glance at other potential causes that might lead you to witness this P0420 code:
- Another common reason behind this P0420 error code on Chevy Silverado is either a Damage exhaust manifold or a leaking in the exhaust system/pipe.
- Besides the internally failed or worn-out catalytic converter, a faulty Oxygen Sensor or air-fuel Sensor can also lead to witnessing this DTC code.
- Engine misfiring, which is also the main culprit of internal converter failure.
- Problem with ignition system, fuel system, or air intake can also damage the catalytic converters.
- When the catalytic converter oil is contaminated or bad, it causes the catalytic system to malfunction and triggers the P0420 code too.
- If the engine coolant temperature sensor is not functioning correctly, you will see this code too.
- If the internal wiring connections wear off or come loose, the P0420 code might show up.
- Fuel injectors leakage, using the wrong type of gasoline, and excess fuel pressure can also cause such a commotion.
Other Symptoms Of Getting P0420 Code On Chevy Silverado
Seeing the P0420 code on your Chevy Silverado is itself an obvious sign, but some other symptoms can also help you detect the problem in advance –
- Check Engine Light illuminate indicates that something might be wrong with the Catalytic converter system. But this warning might also get triggered by other internal problematic issues. So, perform a proper diagnosis with a DTC diagnostic tool to confirm it.
- Another potential sign of catalytic converter malfunctioning or failure is when you notice the engine does not run smoothly and fails to produce enough power on acceleration.
- You will notice a significant decrease in fuel economy where you won’t be able to speed up your vehicle more than 30 to 40 mph even on the highways or freeways.
- If sulfur or rotten egg odor is coming from your vehicle’s exhaust pipe, that means the catalytic converter has an incorrect amount of oxygen which causes this bad smell coming from the exhaust system.
How To Fix The P0420 Code On The Chevy Silverado?
Once you have noticed or received the P0420 Diagnostic Trouble code on your Chevy Silverado vehicle, you can easily fix it at home by following these instructions:
The 3-minute DIY solutions (3 different Method & Estimated cost $19.66)
1. Download The ZUS App & Verify The Error Code
First, download the ZUS app on your mobile phone and scan to verify the error code.
If you are seeing the P0420 error code, it means that the ECM has tested the oxygen sensor heater circuit of your Chevy Silverado and detected an issue with the Bank 1 Sensor 1.
2. Cleaning The Catalytic Converter
This is the first method that you can try after confirming the P0420 error code and following the below instructions to clean the converter:
First, get a Catalytic Converter Cleaner and pour the cleaner liquid into the gas tank.
Next, run your vehicle 150 miles or run the vehicle engine at about 2500 RPMs for 30 minutes to let the cleaner run through to revive the converter.
3. Washing The Catalytic Converter
Carefully remove the catalytic converter assembly from your vehicle first.
If you do not know how to remove the converter, watch this video to learn the step-by-step instructions: https://youtu.be/vWud_tKWU54?t=1
Bring a bucket and put soapy water in it by mixing the detergent powder with water.
Once the mixture has foamed up well, put the catalytic converter into the solution.
Let it soak for at least 10 hours to remove all the built-up residues and curd.
Take the catalytic converter out of that solution and check whether the converter is properly cleaned or not.
Let the converter dry up properly before putting it back in your vehicle, and securely place the catalytic converter back again.
4. Modifying The Oxygen Sensor
First, remove the oxygen sensor from the converter.
Then, use a non-fouler spark plug and refit it with a half-inch drill to put some extra space between the sensor and the converter.
Now re-insert them back in securely.
How Much Does It Cost To Fix The Chevy Silverado P0420 Code?
In general, repairing or fixing the P0420 error code on any vehicle can cost a minimum of $10 up to $2000 or more. (The parts price can vary depending on which Chevy Silverado model you are using)
| Required Replacement | Estimated Parts Prices | Estimated Labor Expenses |
| Air-fuel Sensor | $150 up to $300 | $88 to $115 |
| Oxygen Sensor | $150 up to $500 | $45 to $60 |
| Catalytic Converter | $500 up to $1500 | $151 to $190 |
| Exhaust Pipe leak | $100 up to $250 | $88 to $111 |
| Repairing Exhaust Manifold | $200 up to $250 | $187 to $236 |
Mechanics will first spend an hour diagnosing your vehicle thoroughly and they add this diagnosis cost with the repairing or servicing cost. The labor expense will hang between $75 and $200 based on the local rate of your area.
Common Mistakes To Avoid While Diagnosing P0420 Code On Chevy Silverado
Most users make some common mistakes while diagnosing the P0420 error code:
- One of the most common mistakes is replacing the oxygen sensor before finishing the whole diagnosis procedures.
- Another one is not reading the user’s repair/troubleshooting manual provided by the manufacturer thoroughly before starting the diagnostic process.
- People often only inspect the oxygen sensors, air fuel sensors and the catalytic converter, but sometimes the P0420 code triggers by any problem occurred in the ignition system, fuel system, and exhaust.
Frequently Asked Questions (FAQs)
Does the P0420 Code On Chevy Silverado affect Its Gas Mileage?
No, this code is generated by PCM to measure the Catalytic Converters efficiency. So, it does not directly affect the fuel economy.
Is It Possible To Fix The Converter Of The Chevy Silverado Without Replacing It?
Yes, you can. In that case, you need to switch to high-octane fuel.
Can I Clean The Catalytic Converter Without Taking It Out?
Yes, you can. But in some cases, the internal connections or parts come loose and you cannot repair or replace them without removing the converter.
Final Thoughts
I have already explained the P0420 definition, what causes this error code to flash, the symptoms to determine the error, and how to fix this error with the easy DIY method.
Thus, next time you witness the code P0420 in the future, do not panic and either follow the DIY instructions to fix it by yourself at home or take your vehicle to the nearest Chevy workshop.
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